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README.md

README.md

Prelude

Bozhidar Batsov (from the upstream original):

One thing has always bothered me as Ruby developer—Python devs have a great programming style reference (PEP-8), and we never got an official guide documenting Ruby coding style and best practices. And I do believe that style matters.

This document was originally created when I, as the Technical Lead of the company which I work for, was asked by our CTO to create some internal documents describing good style and best practices for Ruby programming. I started off by building upon this existing style guide, since I concurred with many of the points in it. At some point I decided that the work I was doing might be interesting to members of the Ruby community in general and that the world had little need of another internal company guideline. But the world could certainly benefit from a community-driven and community-sanctioned set of practices, idioms and style prescriptions for Ruby programming.

Since the inception of the guide I've received a lot of feedback from members of the exceptional Ruby community around the world. Thanks for all the suggestions and the support! Together we can make a resource beneficial to each and every Ruby developer out there.

The Ruby Style Guide

This Ruby style guide recommends best practices so that real-world Ruby programmers can write code that can be maintained by other real-world Ruby programmers. A style guide that reflects real-world usage gets used, and a style guide that holds to an ideal that has been rejected by the people it is supposed to help risks not getting used at all – no matter how good it is.

The guide is separated into several sections of related rules. I've tried to add the rationale behind the rules (if it's omitted I've assumed that is pretty obvious).

I didn't come up with all the rules out of nowhere - they are mostly based on my extensive career as a professional software engineer, feedback and suggestions from members of the Ruby community and various highly regarded Ruby programming resources, such as "Programming Ruby 1.9" and "The Ruby Programming Language".

The guide is still a work in progress - some rules are lacking examples, some rules don't have examples that illustrate them clearly enough. In due time these issues will be addressed - just keep them in mind for now.

You can generate a PDF or an HTML copy of this guide using Transmuter.

Table of Contents

Source Code Layout

Nearly everybody is convinced that every style but their own is ugly and unreadable. Leave out the "but their own" and they're probably right...
-- Jerry Coffin (on indentation)

  • Use UTF-8 as the source file encoding.
  • Use two spaces per indentation level.

    # good
    def some_method
      do_something
    end
    
    # bad - four spaces
    def some_method
        do_something
    end
  • Use Unix-style line endings. (*BSD/Solaris/Linux/OSX users are covered by default, Windows users have to be extra careful.)

    • If you're using Git you might want to add the following configuration setting to protect your project from Windows line endings creeping in:

      ```
      $ git config --global core.autocrlf true
      ```
      
  • Use spaces around operators, after commas, colons and semicolons, around { and before }. Whitespace might be (mostly) irrelevant to the Ruby interpreter, but its proper use is the key to writing easily readable code.

      sum = 1 + 2
      a, b = 1, 2
      1 > 2 ? true : false; puts 'Hi'
      [1, 2, 3].each { |e| puts e }

    The only exception is when using the exponent operator:

      # bad
      e = M * c ** 2
    
      # good
      e = M * c**2
  • No spaces after (, [ or before ], ).

    some(arg).other
    [1, 2, 3].length
  • Indent when as deep as case. I know that many would disagree with this one, but it's the style established in both the "The Ruby Programming Language" and "Programming Ruby".

      case
      when song.name == 'Misty'
        puts 'Not again!'
      when song.duration > 120
        puts 'Too long!'
      when Time.now.hour > 21
        puts %q(It's too late)
      else
        song.play
      end
    
      kind = case year
             when 1850..1889 then 'Blues'
             when 1890..1909 then 'Ragtime'
             when 1910..1929 then 'New Orleans Jazz'
             when 1930..1939 then 'Swing'
             when 1940..1950 then 'Bebop'
             else 'Jazz'
             end
  • Use empty lines between defs and to break up a method into logical paragraphs.

      def some_method
        data = initialize(options)
    
        data.manipulate!
    
        data.result
      end
    
      def some_method
        result
      end
  • Align the parameters of a method call if they span over multiple lines.

    # starting point (line is too long)
    def send_mail(source)
      Mailer.deliver(to: 'bob@example.com', from: 'us@example.com', subject: 'Important message', body: source.text)
    end
    
    # bad (normal indent)
    def send_mail(source)
      Mailer.deliver(
        to: 'bob@example.com',
        from: 'us@example.com',
        subject: 'Important message',
        body: source.text)
    end
    
    # bad (double indent)
    def send_mail(source)
      Mailer.deliver(
          to: 'bob@example.com',
          from: 'us@example.com',
          subject: 'Important message',
          body: source.text)
    end
    
    # good
    def send_mail(source)
      Mailer.deliver(to: 'bob@example.com',
                     from: 'us@example.com',
                     subject: 'Important message',
                     body: source.text)
    end
  • Use RDoc and its conventions for API documentation. Don't put an empty line between the comment block and the def.

  • Keep lines fewer than 100 characters.
  • Avoid trailing whitespace.

Syntax

  • Use def with parentheses when there are arguments. Omit the parentheses when the method doesn't accept any arguments.

       def some_method
         # body omitted
       end
    
       def some_method_with_arguments(arg1, arg2)
         # body omitted
       end
  • Never use for, unless you know exactly why. Most of the time iterators should be used instead. for is implemented in terms of each (so you're adding a level of indirection), but with a twist - for doesn't introduce a new scope (unlike each) and variables defined in its block will be visible outside it.

      arr = [1, 2, 3]
    
      # bad
      for elem in arr do
        puts elem
      end
    
      # good
      arr.each { |elem| puts elem }
  • Never use then for multi-line if/unless.

    # bad
    if some_condition then
      # body omitted
    end
    
    # good
    if some_condition
      # body omitted
    end
  • Favor the ternary operator(?:) over if/then/else/end constructs. It's more common and obviously more concise.

      # bad
      result = if some_condition then something else something_else end
    
      # good
      result = some_condition ? something : something_else
  • Use one expression per branch in a ternary operator. This also means that ternary operators must not be nested. Prefer if/else constructs in these cases.

      # bad
      some_condition ? (nested_condition ? nested_something : nested_something_else) : something_else
    
      # good
      if some_condition
        nested_condition ? nested_something : nested_something_else
      else
        something_else
      end
  • Never use if x: ... — it is removed in Ruby 1.9. Use the ternary operator instead.

    # bad
    result = if some_condition: something else something_else end
    
    # good
    result = some_condition ? something : something_else
  • Never use if x; .... Use the ternary operator instead.

  • Avoid multi-line x ? a : b (the ternary operator), use if/unless instead.
  • Use when x then ... for one-line cases. The alternative syntax when x: ... is removed in Ruby 1.9. The same is true for the when x; ... syntax.
  • Use && and || for boolean expressions, and and or for control flow. (Rule of thumb: if you have to use outer parentheses, you are using the wrong operators.)

      # boolean expression
      if some_condition && some_other_condition
        do_something
      end
    
      # control flow
      document.saved? or document.save!
  • Avoid multi-line ?: (the ternary operator), use if/unless instead.

  • Favor modifier if/unless usage when you have a single-line body. Another good alternative is the usage of control flow and/or.

      # bad
      if some_condition
        do_something
      end
    
      # good
      do_something if some_condition
    
      # another good option:
      some_condition and do_something
  • Favor unless over if for negative conditions (or control flow or).

    # bad
    do_something if !some_condition
    
    # good
    do_something unless some_condition
    
    # another good option:
    some_condition or do_something
  • Never use unless with else. Rewrite these with the positive case first.

    # bad
    unless success?
      puts 'failure'
    else
      puts 'success'
    end
    
    # good
    if success?
      puts 'success'
    else
      puts 'failure'
    end
  • Don't use parentheses around the condition of an if/unless/while, unless the condition contains an assignment (see "Using the return value of =" below).

      # bad
      if (x > 10)
        # body omitted
      end
    
      # good
      if x > 10
        # body omitted
      end
    
      # ok
      if (x = self.next_value)
        # body omitted
      end
  • Favor modifier while/until usage when you have a single-line body.

      # bad
      while some_condition
        do_something
      end
    
      # good
      do_something while some_condition
  • Favor until over while for negative conditions.

    # bad
    do_something while !some_condition
    
    # good
    do_something until some_condition
  • Omit parentheses around parameters for methods where not required. Use parentheses around the arguments when utilizing the return value or when chaining method invocations.

      class Person
        attr_reader :name, :age # omitted
      end
    
      temperance = Person.new('Temperance', 30)
      temperance.name
    
      puts temperance.age
    
      x = Math.sin(y)
      array.delete e
  • Prefer {...} over do...end for single-line blocks. Avoid using {...} for multi-line blocks (multiline chaining is always ugly). Always use do...end for "control flow" and "method definitions" (e.g. in Rakefiles and certain DSLs). Avoid do...end when chaining.

      names = ['Bozhidar', 'Steve', 'Sarah']
    
      # good
      names.each { |name| puts name }
    
      # bad
      names.each do |name|
        puts name
      end
    
      # good
      names.select { |name| name.start_with?('S') }.map { |name| name.upcase }
    
      # bad
      names.select do |name|
        name.start_with?('S')
      end.map { |name| name.upcase }

    Some will argue that multiline chaining would look OK with the use of {...}, but they should ask themselves - it this code really readable and can't the blocks contents be extracted into nifty methods.

  • Use return freely where it is useful for clarity.

  • Avoid self where not required.

    # bad
    def ready?
      if self.last_reviewed_at > self.last_updated_at
        self.worker.update(self.content, self.options)
        self.status = :in_progress
      end
      self.status == :verified
    end
    
    # good
    def ready?
      if last_reviewed_at > last_updated_at
        worker.update(content, options)
        self.status = :in_progress
      end
      status == :verified
    end
  • As a corollary, avoid shadowing methods with local variables unless they are both equivalent

    class Foo
      attr_accessor :options
    
      # ok
      def initialize(options)
        self.options = options
        # both options and self.options are equivalent here
      end
    
      # bad
      def do_something(options = {})
        unless options[:when] == :later
          output(self.options[:message])
        end
      end
    
      # good
      def do_something(params = {})
        unless params[:when] == :later
          output(options[:message])
        end
      end
    end
    
    * Use spaces around the `=` operator when assigning default values to method parameters:
    
    ```Ruby
    # bad
    def some_method(arg1=:default, arg2=nil, arg3=[])
      # do something...
    end
    
    # good
    def some_method(arg1 = :default, arg2 = nil, arg3 = [])
      # do something...
    end

    While several Ruby books suggest the first style, the second is much more prominent in practice (and arguably a bit more readable).

    • Avoid line continuation (\) where not required. In practice, avoid using line continuations at all.

      # bad
      result = 1 - \
               2
      
      # only slightly better (but still ugly as hell)
      result = 1 \
               - 2
    • Using the return value of = (an assignment) is ok, but surround the assignment with parenthesis.

      # good - shows intended use of assignment
      if (v = array.grep(/foo/)) ...
      
      # bad
      if v = array.grep(/foo/) ...
      
      # also good - shows intended use of assignment and has correct precedence.
      if (v = self.next_value) == 'hello' ...
    • Use ||= freely to initialize variables.

    # set name to Bozhidar, only if it's nil or false
    name ||= 'Bozhidar'
    • Avoid using Perl-style special variables (like $0-9, $`, etc. ). They are quite cryptic and their use in anything but one-liner scripts is discouraged.

    • Never put a space between a method name and the opening parenthesis.

    # bad
    puts (3 + 2) + 1
    
    # good
    puts(3 + 2) + 1
    • If the first argument to a method begins with an open parenthesis, always use parentheses in the method invocation.
    puts((3 + 2) + 1)
    • Always run the Ruby interpreter with the -w option so it will warn you if you forget either of the rules above!

    • When the keys of your hash are symbols use the Ruby 1.9 hash literal syntax.

    # bad
    hash = { :one => 1, :two => 2 }
    
    # good
    hash = { one: 1, two: 2 }
    • Use the new lambda literal syntax.
    # bad
    lambda = lambda { |a, b| a + b }
    lambda.call(1, 2)
    
    # good
    lambda = ->(a, b) { a + b }
    lambda.(1, 2)
    • Use _ for unused block parameters.
    # bad
    result = hash.map { |k, v| v + 1 }
    
    # good
    result = hash.map { |_, v| v + 1 }

    Naming

    The only real difficulties in programming are cache invalidation and naming things.
    -- Phil Karlton

    • Use snake_case for methods and variables.
    • Use CamelCase for classes and modules. (Keep acronyms like HTTP, RFC, XML uppercase.)
    • Use SCREAMING_SNAKE_CASE for other constants.
    • The names of predicate methods (methods that return a boolean value) should end in a question mark. (i.e. Array#empty?).
    • The names of potentially "dangerous" methods (i.e. methods that modify self or the arguments, exit! (doesn't run the finalizers like exit does), etc.) should end with an exclamation mark if there exists a safe version of that dangerous method.

      # bad - there is not matching 'safe' method
      class Person
        def update!
        end
      end
      
      # good
      class Person
        def update
        end
      end
      
      # good
      class Person
        def update!
        end
      
        def update
        end
      end
    • Define the non-bang (safe) method in terms of the bang (dangerous) one if possible.

      class Array
        def flatten_once!
          res = []
      
          each do |e|
            [*e].each { |f| res << f }
          end
      
          replace(res)
        end
      
        def flatten_once
          dup.flatten_once!
        end
      end
    • When using reduce with short blocks, name the arguments |a, e| (accumulator, element).

    • When defining binary operators, name the argument other.
    def +(other)
      # body omitted
    end
    • Prefer map over collect, find over detect, select over find_all, reduce over inject and size over length. This is not a hard requirement; if the use of the alias enhances readability, it's ok to use it. The rhyming methods are inherited from Smalltalk and are not common in other programming languages. The reason the use of select is encouraged over find_all is that it goes together nicely with reject and its name is pretty self-explanatory.

    Comments

    Good code is its own best documentation. As you're about to add a comment, ask yourself, "How can I improve the code so that this comment isn't needed?" Improve the code and then document it to make it even clearer.
    -- Steve McConnell

    • In comments written using #, # should be followed by a space.
    • Comments longer than a word are capitalized and use proper punctuation and grammar. Use one space after periods.
    • Avoid superfluous comments.
    # bad
    counter += 1 # increments counter by one
    • Keep existing comments up-to-date. An outdated is worse than no comment at all.

    Good code is like a good joke - it needs no explanation.
    -- Russ Olsen

    • Avoid writing comments to explain bad code. Refactor the code to make it self-explanatory. (Do or do not - there is no try. --Yoda)

    Annotations

    • Annotations should usually be written on the line immediately above the relevant code.
    • The annotation keyword is followed by a colon and a space, then a note describing the problem.
    • If multiple lines are required to describe the problem, subsequent lines should be indented two spaces after the #.

      def bar
        # FIXME: This has crashed occasionally since v3.2.1. It may
        #   be related to the BarBazUtil upgrade.
        baz :quux
      end
    • In cases where the problem is so obvious that any documentation would be redundant, annotations may be left at the end of the offending line with no note. This usage should be the exception and not the rule.

      def bar
        sleep 100 # OPTIMIZE
      end
    • Use TODO to note missing features or functionality that should be added at a later date.

    • Use FIXME to note broken code that needs to be fixed.
    • Use OPTIMIZE to note slow or inefficient code that may cause performance problems.
    • Use REFACTOR to note code smells where questionable coding practices were used and should be refactored away.
    • Use REVIEW to note anything that should be looked at to confirm it is working as intended. For example:

      # REVIEW: Are we sure this is how the client does X currently?
    • Use other custom annotation keywords if it feels appropriate, but be sure to document them in the project's README file.

    Classes

    • When designing class hierarchies make sure that they conform to the Liskov Substitution Principle.
    • Try to make your classes as [SOLID](http://en.wikipedia.org/wiki/SOLID_(object-oriented_design\)) as possible.
    • Always supply a proper to_s method for classes that represent domain objects.

      class Person
        attr_reader :first_name, :last_name
      
        def initialize(first_name, last_name)
          @first_name = first_name
          @last_name = last_name
        end
      
        def to_s
          "#@first_name #@last_name"
        end
      end
    • Use the attr family of functions to define trivial accessors or mutators.

    # bad
    class Person
      def initialize(first_name, last_name)
        @first_name = first_name
        @last_name = last_name
      end
    
      def first_name
        @first_name
      end
    
      def last_name
        @last_name
      end
    end
    
    # good
    class Person
      attr_reader :first_name, :last_name
    
      def initialize(first_name, last_name)
        @first_name = first_name
        @last_name = last_name
      end
    end
    • Consider using Struct.new, which defines the trivial accessors, constructor and comparison operators for you.
    # good
    class Person
      attr_reader :first_name, :last_name
    
      def initialize(first_name, last_name)
        @first_name = first_name
        @last_name = last_name
      end
    end
    
    # better
    class Person < Struct.new (:first_name, :last_name)
    end
    • Consider adding factory methods to provide additional sensible ways to create instances of a particular class.
    class Person
      def self.create(options_hash)
        # body omitted
      end
    end
    # bad
    class Animal
      # abstract method
      def speak
      end
    end
    
    # extend superclass
    class Duck < Animal
      def speak
        puts 'Quack! Quack'
      end
    end
    
    # extend superclass
    class Dog < Animal
      def speak
        puts 'Bau! Bau!'
      end
    end
    
    # good
    class Duck
      def speak
        puts 'Quack! Quack'
      end
    end
    
    class Dog
      def speak
        puts 'Bau! Bau!'
      end
    end
    • Avoid the usage of class (@@) variables due to their "nasty" behavior in inheritance.
    class Parent
      @@class_var = 'parent'
    
      def self.print_class_var
        puts @@class_var
      end
    end
    
    class Child < Parent
      @@class_var = 'child'
    end
    
    Parent.print_class_var # => will print "child"

    As you can see all the classes in a class hierarchy actually share one class variable. Class instance variables should usually be preferred over class variables.

    • Assign proper visibility levels to methods (private, protected) in accordance with their intended usage. Don't go off leaving everything public (which is the default). After all we're coding in Ruby now, not in Python.
    • Indent the public, protected, and private methods as much the method definitions they apply to. Leave one blank line above them.

      class SomeClass
        def public_method
          # ...
        end
      
        private
      
        def private_method
          # ...
        end
      end
    • Use def self.method to define singleton methods. This makes the methods more resistant to refactoring changes.

      class TestClass
        # bad
        def TestClass.some_method
          # ...
        end
      
        # good
        def self.some_other_method
          # ...
        end
      
        # Also possible and convenient when you have to define many singleton methods:
        class << self
          def first_method
            # ...
          end
      
          def second_method_etc
            # ...
          end
        end
      end

    Exceptions

    • Signal exceptions using the fail keyword. Use raise only when catching an exception and re-raising it (because here you're not failing, but explicitly and purposefully raising an exception).

      begin
        fail 'Oops';
      rescue => error
        raise if error.message != 'Oops'
      end
    • Never return form an ensure block. If you explicitly return from a method inside an ensure block, the return will take precedence over any exception being raised, and the method will return as if no exception had been raised at all. In effect, the exception will be silently thrown away.

      def foo
        begin
          fail
        ensure
          return 'very bad idea'
        end
      end
    • Use implicit begin blocks when possible.

    # bad
    def foo
      begin
        # main logic goes here
      rescue
        # failure handling goes here
      end
    end
    
    # good
    def foo
      # main logic goes here
    rescue
      # failure handling goes here
    end
    • Mitigate the proliferation of begin blocks via the use of contingency methods (a term coined by Avdi Grimm).

      # bad
      begin
        something_that_might_fail
      rescue IOError
        # handle IOError
      end
      
      begin
        something_else_that_might_fail
      rescue IOError
        # handle IOError
      end
      
      # good
      def with_io_error_handling
         yield
      rescue
        # handle IOError
      end
      
      with_io_error_handling { something_that_might_fail }
      
      with_io_error_handling { something_else_that_might_fail }
    • Don't suppress exceptions.

    # bad
    begin
      # an exception occurs here
    rescue SomeError
      # the rescue clause does absolutely nothing
    end
    
    # bad
    do_something rescue nil
    • Don't use exceptions for flow of control.
    # bad
    begin
      n / d
    rescue ZeroDivisionError
      puts 'Cannot divide by 0!'
    end
    
    # good
    if d.zero?
      puts 'Cannot divide by 0!'
    else
      n / d
    end
    • Avoid rescuing the Exception class. This will trap signals and calls to exit, requiring you to kill -9 the process.

      # bad
      begin
        # calls to exit and kill signals will be caught (except kill -9)
        exit
      rescue Exception
        puts "you didn't really want to exit, right?"
        # exception handling
      end
      
      # good
      begin
        # a blind rescue rescues from StandardError, not Exception as many
        # programmers assume.
      rescue => e
        # exception handling
      end
      
      # also good
      begin
        # an exception occurs here
      
      rescue StandardError => e
        # exception handling
      end
      
    • Put more specific exceptions higher up the rescue chain, otherwise they'll never be rescued from.

      # bad
      begin
        # some code
      rescue Exception => e
        # some handling
      rescue StandardError => e
        # some handling
      end
      
      # good
      begin
        # some code
      rescue StandardError => e
        # some handling
      rescue Exception => e
        # some handling
      end
    • Release external resources obtained by your program in an ensure block.

    f = File.open('testfile')
    begin
      # .. process
    rescue
      # .. handle error
    ensure
      f.close unless f.nil?
    end
    • Favor the use of exceptions for the standard library over introducing new exception classes.

    Collections

    • Prefer literal array and hash creation notation (unless you need to pass parameters to their constructors, that is).
    # bad
    arr = Array.new
    hash = Hash.new
    
    # good
    arr = []
    hash = {}
    • Prefer %w to the literal array syntax when you need an array of strings.
    # bad
    STATES = ['draft', 'open', 'closed']
    
    # good
    STATES = %w(draft open closed)
    • Avoid the creation of huge gaps in arrays.
    arr = []
    arr[100] = 1 # now you have an array with lots of nils
    • Use Set instead of Array when dealing with unique elements. Set implements a collection of unordered values with no duplicates. This is a hybrid of Array's intuitive inter-operation facilities and Hash's fast lookup.
    • Use symbols instead of strings as hash keys.
    # bad
    hash = { 'one' => 1, 'two' => 2, 'three' => 3 }
    
    # good
    hash = { one: 1, two: 2, three: 3 }
    • Avoid the use of mutable object as hash keys.
    • Use the new 1.9 literal hash syntax in preference to the hashrocket syntax.
    # bad
    hash = { :one => 1, :two => 2, :three => 3 }
    
    # good
    hash = { one: 1, two: 2, three: 3 }
    • Rely on the fact that hashes in 1.9 are ordered.
    • Never modify a collection while traversing it.

    Strings

    • Prefer string interpolation instead of string concatenation:
    # bad
    email_with_name = user.name + ' <' + user.email + '>'
    
    # good
    email_with_name = "#{user.name} <#{user.email}>"
    • Consider padding string interpolation code with space. It more clearly sets the code apart from the string.

      "#{ user.last_name }, #{ user.first_name }"
    • Prefer single-quoted strings when you don't need string interpolation or special symbols such as \t, \n, ', etc.

      # bad
      name = "Bozhidar"
      
      # good
      name = 'Bozhidar'
    • Don't use {} around instance variables being interpolated into a string.

      class Person
        attr_reader :first_name, :last_name
      
        def initialize(first_name, last_name)
          @first_name = first_name
          @last_name = last_name
        end
      
        # bad
        def to_s
          "#{@first_name} #{@last_name}"
        end
      
        # good
        def to_s
          "#@first_name #@last_name"
        end
      end
    • Avoid using String#+ when you need to construct large data chunks. Instead, use String#<<. Concatenation mutates the string instance in-place and is always faster than String#+, which creates a bunch of new string objects.

      # good and also fast
      html = ''
      html << '<h1>Page title</h1>'
      
      paragraphs.each do |paragraph|
        html << "<p>#{paragraph}</p>"
      end
    • For multi-line strings, prefer heredoc.
    # Okay
    output =  'Lorem ipsum dolor sit amet, consectetur adipiscing elit. Donec posuere, nisi nec'
    ouptut << 'molestie feugiat, libero lectus sollicitudin risus, vitae fermentum diam velit at'
    output << foo
    output << 'ante. Nullam vitae massa semper velit vestibulum scelerisque. Ut justo metus,'
    output << "dictum #{bar} non congue placerat, eleifend non felis. Pellentesque erat lectus."
    puts output
    
    
    # Better (avoids ever storing the variable; easier to read and work with)
    puts <<-OUTPUT.strip_heredoc
      Lorem ipsum dolor sit amet, consectetur adipiscing elit. Donec posuere, nisi nec molestie
      feugiat, libero lectus sollicitudin risus, vitae fermentum diam velit at #{foo} ante. Nullam
      vitae massa semper velit vestibulum scelerisque. Ut justo metus, dictum #{bar} non congue
      placerat, eleifend non felis. Pellentesque erat lectus, luctus sit amet.
    OUTPUT

    Regular Expressions

    • Don't use regular expressions if you just need plain text search in string: string['text']
    • For simple constructions you can use regexp directly through string index.
    match = string[/regexp/]             # get content of matched regexp
    first_group = string[/text(grp)/, 1] # get content of captured group
    string[/text (grp)/, 1] = 'replace'  # string => 'text replace'
    • Use non capturing groups when you don't use captured result of parenthesis.
    /(first|second)/   # bad
    /(?:first|second)/ # good
    • Avoid using $1-9 as it can be hard to track what they contain. Named groups can be used instead.

      # bad
      /(regexp)/ =~ string
      ...
      process $1
      
      # good
      /(?<meaningful_var>regexp)/ =~ string
      ...
      process meaningful_var
    • Character classes have only few special characters you should care about: ^, -, \, ], so don't escape . or brackets in [].

    • Be careful with ^ and $ as they match start/end of line, not string endings. If you want to match the whole string use: \A and \z (not to be confused with \Z which is the equivalent of /\n?\z/).

      string = "some injection\nusername"
      string[/^username$/]   # matches
      string[/\Ausername\z/] # don't match
    • Use x modifier for complex regexps. This makes them more readable and you can add some useful comments. Just be careful as spaces are ignored.

      regexp = %r{
        start         # some text
        \s            # white space char
        (group)       # first group
        (?:alt1|alt2) # some alternation
        end
      }x
    • For complex replacements sub/gsub can be used with block or hash.

    Percent Literals

    • Use %w or %W freely.
    STATES = %w(draft open closed)
    • Use %Q or %() freely. Remember to use %q for cases that require no interpolation.
    %q(<div class="text">Some text</div>)
    %(This is #{quality} style)
    %Q(<div>\n<span class="big">#{exclamation}</span>\n</div>)
    %[<tr><td class="name">#{name}</td>]
    • Avoid use of confusing delimiters with any of the % literals:
    %q"non-interpereted string"
    %'interepeted'
    %w/not a regex/
    • Use %r for regular expressions matching / characters.
    # bad
    /^\/blog\/2011\/(.*)$/
    
    # good
    %r(^/blog/2011/(.*)$)
    • Prefer (), [] or {} as delimiters for all % literals.

    Metaprogramming

    • Do not mess around in core classes when writing libraries. (Do not monkey patch them.)

    • The block form of class_eval is preferable to the string-interpolated form.

    • when you use the string-interpolated form, always supply __FILE__ and __LINE__, so that your backtraces make sense:

      class_eval 'def use_relative_model_naming?; true; end', __FILE__, __LINE__
    • define_method is preferable to class_eval{ def ... }

    • When using class_eval (or other eval) with string interpolation, add a comment block showing its appearance if interpolated (a practice I learned from the rails code):

    # from activesupport/lib/active_support/core_ext/string/output_safety.rb
    UNSAFE_STRING_METHODS.each do |unsafe_method|
      if 'String'.respond_to?(unsafe_method)
        class_eval <<-EOT, __FILE__, __LINE__ + 1
          def #{unsafe_method}(*args, &block)       # def capitalize(*args, &block)
            to_str.#{unsafe_method}(*args, &block)  #   to_str.capitalize(*args, &block)
          end                                       # end
    
          def #{unsafe_method}!(*args)              # def capitalize!(*args)
            @dirty = true                           #   @dirty = true
            super                                   #   super
          end                                       # end
        EOT
      end
    end

    Misc

    • Write ruby -w safe code; that is, execute files with ruby -w -c to check syntax before committing.
    • Avoid parameter lists longer than three or four parameters.
    • If you really have to, add "global" methods to Kernel and make them private. Otherwise, never use global variables within Rails.
    • Use class instance variables instead of global variables.
    #bad
    $foo_bar = 1
    
    #good
    class Foo
      class << self
        attr_accessor :bar
      end
    end
    
    Foo.bar = 1
    • Avoid alias when alias_method will do.
    • Use OptionParser for parsing complex command line options and ruby -s for trivial command line options.
    • Avoid needless metaprogramming.

    Design

    Contributing

    Nothing written in this guide is set in stone. I intend this document to be a suggestion. I expect the rest of the team have their own opinions about what is ideal code style.

    There are a few elements from the original that I left, here, even though they don't apply to our needs.

    Feel free to change stuff to your liking!

    Spread the Word

    This style guide was written by Bozhidar Batsov, then modified by Ryan Long.

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